Method of treating a preceramic material

ABSTRACT

A method of treating a preceramic material includes providing a preceramic polycarbosilane or polycarbosiloxane material that includes a moiety Si—O—M, where Si is silicon, O is oxygen and M is at least one metal, and thermally converting the preceramic polycarbosilane or polycarbosiloxane that includes the moiety Si—O—M material into a ceramic material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/352,584, filed Jan. 18, 2012.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract numberN00014-09-C-0201 awarded by the United States Navy. The government hascertain rights in the invention.

BACKGROUND

This disclosure relates to processing of preceramic materials and, moreparticularly, to treating a preceramic polymer material.

Machine components, such as components of gas turbine engines, aresubjected to high temperatures, corrosive and oxidative conditions andelevated stress levels. In order to improve the thermal and oxidativestability of such components, the components may include a thermallyresistant ceramic material. There are different ceramic processingtechniques for forming ceramic material, including thermal conversion ofa preceramic polymer.

SUMMARY

A method of treating a preceramic material according to a non-limitingexample of the present disclosure includes providing a preceramicpolycarbosilane or polycarbosiloxane material that includes a moietySi—O—M and thermally converting the preceramic polycarbosilane orpolycarbosiloxane material that includes the moiety Si—O—M into aceramic material.

A further embodiment of the foregoing method includes thermallyconverting the preceramic polycarbosilane or polycarbosiloxane materialproduces a ceramic material having a composition SiO_(x)M_(z)C_(y),wherein x<2, y >0 and z<1 and x and z are non-zero.

In a further embodiment of the foregoing method, the at least one metalis selected from the group consisting of aluminum, boron, alkaline earthmetals, transition metals, refractory metals, rare earth metals andcombinations thereof.

In a further embodiment of the foregoing method, the at least one metalis selected from the group consisting of aluminum, boron andcombinations thereof.

In a further embodiment of the foregoing method, the at least one metalis a transition metal selected from the group consisting of titanium,zirconium, hafnium, vanadium, chromium and combinations thereof.

In a further embodiment of the foregoing method, the at least one metalis a refractory metal selected from the group consisting of niobium,tantalum, molybdenum, tungsten, rhenium and combinations thereof.

In a further embodiment of the foregoing method, the at least one metalis a rare earth metal selected from the group consisting of scandium,ytterbium, gadolinium, yttrium, lanthanum, neodymium, dysprosium,lutetium and combinations thereof.

In a further embodiment of the foregoing method, the at least one metalis an alkaline earth metal selected from the group consisting of barium,strontium, calcium, magnesium, and combinations thereof.

In a further embodiment of the foregoing method, the at least one metalincludes aluminum.

In a further embodiment of the foregoing method, the ceramic materialfrom the thermal converting includes 0.5-20 at. % of the at least onemetal.

In a further embodiment of the foregoing method, the ceramic materialfrom the thermal converting includes 1-10 at. % of the at least onemetal.

A further embodiment of the foregoing method includes crushing theceramic material from the thermal converting to produce a particulatematerial.

A further embodiment of the foregoing method includes thermally treatingthe particulate material in an inert environment.

A further embodiment of the foregoing method includes thermally treatingthe particulate material in an oxidizing environment.

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As will be described, disclosed is a method of treating a preceramicmaterial. The method includes modifying a moiety Si—O—R of apolycarbosilane or polycarbosiloxane material with at least one metal(M), where Si is silicon, O is oxygen and R includes an alkyl or arylmoiety, by reaction to substitute R with M to produce a preceramicpolycarbosilane or polycarbosiloxane material that includes a moietySi—O—M (hereafter “preceramic polycarbosilane” or “preceramicpolycarbosiloxane” material, respectively).

Upon eventual thermal conversion of the preceramic polycarbosilane orpolycarbosiloxane material into a ceramic material, the metal forms athermally stable glass or crystalline ceramic compound or both in themicrostructure. For example, the microstructure of the resulting ceramicmaterial includes regions of glass or crystalline ceramic that includethe metal. The glass or crystalline ceramic regions are dispersed withinregions of Si—O—C ceramic material. The glass can be a low melting pointglass relative to the surrounding Si—O—C ceramic material, which servesto seal microcracks and getter oxygen within the microstructure and thusimproves the properties, durability and densification of the ceramicmaterial in oxidizing environments.

In examples based upon boron or aluminum, the glass is borosilicate oraluminosilicate glass, respectively, or both if boron and aluminum areused as the metal. The glass can have a local melting temperature thatis lower than the surrounding Si—O—C regions. The low melting pointglass regions thereby soften or melt upon exposure to elevatedtemperatures and are thus able to move into microcracks to seal thoseareas. Additionally, the presence of the metal also serves to getteroxygen in-situ and thus intercepts oxygen that might otherwise react toform unfavorable or undesired phases.

The selected metal or metals preserve the glass-forming capability andthe crystallization behavior of the ceramic material that forms from thepreceramic polycarbosilane or polycarbosiloxane material. In this sense,and herein, a glass is defined as an amorphous, generallynon-crystalline, oxygen-containing solid with minimal long rangestructural order. The metal-containing glass of this example may alsoreadily and further oxidize upon exposure to environmental oxidizingconditions, such as the environmental operating conditions within a gasturbine engine, further forming a glassy or crystalline oxide product.Thus, it is to be understood that the composition can change uponoxidation.

As a comparison, Si—O—C alone, without the glass and metal, is subjectto detrimental reactions with elements from the operating environmental,such as oxygen, under relatively high environmental temperatures in thepresence of moisture. The disclosed method yields a preceramicpolycarbosilane or polycarbosiloxane material that can ultimately bethermally converted into a ceramic material having enhanced durability.

In the disclosed method, the moiety Si—O—R of the polycarbosilane orpolycarbosiloxane material is reactive such that the metal can besubstituted for the alkyl or aryl moiety R to produce the preceramicpolycarbosilane or polycarbosiloxane material. Thus, the metal becomescovalently incorporated into the polymeric structure prior to thermalconversion of the material to produce a ceramic material.

In one embodiment, the reaction sequence to substitute the alkyl or arylmoiety R with the metal M includes at least one of a hydrolysis and acondensation reaction.

In one example reaction sequence that includes both a hydrolysisreaction and a condensation reaction, the polycarbosilane orpolycarbosiloxane material having the moiety Si—O—R is alkoxy-modifiedpolycarbosilane or polycarbosiloxane and is reacted with a metal alkoxyor aryloxy compound. In the reaction, the metal of the metal alkoxy oraryloxy compound supplants the alkyl or aryl moiety R to produce themoiety Si—O—M in the preceramic polycarbosilane or polycarbosiloxanematerial.

In embodiments, the alkoxy-modified polycarbosilane material is selectedfrom dimethoxypolycarbosilane, diethoxypolycarbosilane,methoxyethoxypolycarbosilane, isopropoxycarbosilane, butoxycarbosilaneor other alkoxy-modified polycarbosilane (available from Starfire®Systems).

In embodiments, the metal alkoxy compound is metal alkoxide. In oneexample based on aluminum as the metal, the metal alkoxide compound isaluminum isopropoxide. In another example based on boron as the metal,the metal alkoxide compound is boron methoxide. Likewise, for othertarget metals, the metal or metals are provided in alkoxy or aryloxycompounds to carry out the reaction.

The metal or metals are selected from aluminum, boron, alkaline earthmetals, transition metals, refractory metals, rare earth metals andcombinations thereof. These metals are glass-forming metals in that theycan be incorporated, for example, through covalent bonding, intooxide-based glasses. As an example, the selected metal or metals areglass-forming metals that can readily and further oxidize upon exposureto environmental oxidizing conditions, such as the environmentaloperating conditions within a gas turbine engine.

In another example, the metal or metals are alkaline earth metalsselected from barium, strontium, calcium or magnesium.

In a further example, the metal or metals are transition metals selectedfrom, titanium, zirconium, hafnium, vanadium, chromium and combinationsthereof.

In another embodiment, the metal or metals are refractory metalsselected from niobium, tantalum, molybdenum, tungsten, rhenium andcombinations thereof.

In another embodiment, the metal or metals are rare earth metals, suchas scandium, ytterbium, gadolinium, yttrium, lanthanum, neodymium,dysprosium, lutetium and combinations thereof.

In further examples, the preceramic polycarbosilane or polycarbosiloxanematerial may additionally include impurities that do not affect theproperties of the material or elements that are unmeasured orundetectable in the material. In other examples, the preceramicpolycarbosilane or polycarbosiloxane material includes any one of theexample metals, to the exclusion of any other metals that are present inmore than trace amounts as inadvertent impurities. In other examples,the preceramic polycarbosilane or polycarbosiloxane material includes aplurality of the example metals, in any combination, to the exclusion ofany other metals that are present in more than trace amounts asinadvertent impurities.

In one embodiment, the reaction to substitute the metal or metals forthe alkyl or aryl moiety R in the polycarbosilane or polycarbosiloxanematerial is conducted within a solvent solution. For example, thestarting polycarbosilane or polycarbosiloxane material and a metalorganic material of the selected metal or metals are dissolved within asolvent. The selected solvent is compatible with the selected startingpolycarbosilane or polycarbosiloxane material and selected metal organicmaterial or materials. That is, the solvent is suitable for dissolvingthe starting polycarbosilane or polycarbosiloxane material and the metalorganic material or materials. For example, the solvent is selected frommethanol, hexane, tetrahydrofuran, 2-methyl-1-propanol and combinationsthereof. In a further example, the solvent is 2-methyl-1-propanol and isable to readily dissolve the polycarbosilane or polycarbosiloxanematerial, the metal organic material or materials and water that may beadded to the solution to control reaction rate.

In one embodiment, the reaction between the starting polycarbosilane orpolycarbosiloxane material and selected metal organic material ormaterials proceeds without the aid of a catalyst. For example, the metalorganic material is aluminum isopropoxide.

In another embodiment, the metal or metals are initially provided as asolid in the solvent. In one example based on aluminum, discretenano-particles of aluminum are provided in the solvent. Thenano-particles may not be soluble in the solvent, but with the additionof isopropyl alcohol to the solution, the aluminum reacts with theisopropyl alcohol to form aluminum isopropoxide. Similarly, other targetmetals can be provided in solid form with reactive solvents to formmetal organic compounds that then react with the startingpolycarbosilane or polycarbosiloxane material.

In another embodiment that uses a catalyzed reaction, the startingpolycarbosilane or polycarbosiloxane material and the metal organicmaterial or materials that are dissolved within the solvent are providedwith a catalyst, such as an acid catalyst, to promote the reaction. Asan example, the acid is or includes hydrochloric acid. Optionally, thereaction rate is controlled by controlling the amount of acid added tothe solution and an amount of water added in the solution. However, ifno acid catalyst is used, the rate of the reaction can alternatively becontrolled by controlling the amount of metal organic material ormaterials that are added in the solution.

In a further embodiment, the reaction rate is controlled by providingatmospheric humidity as the source of water rather than adding water tothe solution. In the above examples, all the reactions may be carriedout at ambient temperature conditions of 65°-75° F. (18°-24° C.).However, it is to be understood that different temperatures canalternatively be used to further control the rate of reaction.

In a further embodiment, the starting polycarbosilane orpolycarbosiloxane material is initially a liquid material that is addedto the solvent to form the solution. Upon the reaction or reactions tosubstitute the metal or metals for the alkyl or aryl moiety R of thepolycarbosilane or polycarbosiloxane material, a solid or semi-solidprecipitant results. Upon completion or substantial completion of thereaction or reactions, the solvent can then be removed, leaving thesolid or semi-solid reaction product. The reaction product is thepreceramic polycarbosilane or polycarbosiloxane material that includesthe moiety Si—O—M. In one embodiment, the resulting solid or semi-solidis further dried under the vacuum and/or at elevated temperatures toremove or substantially remove all of the solvent.

In a further embodiment, the preceramic polycarbosilane orpolycarbosiloxane material is then further processed to produce aceramic material. As an example, the preceramic polycarbosilane orpolycarbosiloxane material is thermally converted into a ceramicmaterial having a composition SiO_(x)M_(z)C_(y), where Si is silicon, Ois oxygen, M is the metal or metals and C is carbon and wherein x<2, y>0and z<1 and x and z are non-zero. It is to be understood that the metalcomposition includes the combined composition of all covalently bondedmetals M.

In one example of thermally converting the preceramic polycarbosilane orpolycarbosiloxane material, the resulting solid or semi-solid from theabove-described reaction or reactions is heated to approximately 1000°C. in air, argon or nitrogen and held for approximately 2 hours toproduce a ceramic material. It is to be understood that differentthermal conversion conditions can be used. However, a combination ofheating and atmospheric exposures can be used if desired. In thisexample, the choice of atmosphere type, exposure time and exposuretemperature is used to control the resulting ceramic phase(s). In oneexample, the ceramic yield is in a range of approximately 60-65 wt. %with regard to the starting mass of the preceramic polycarbosilane orpolycarbosiloxane material. In a further example, the metal constitutesapproximately 0.5-20 at. % of the resulting ceramic material, and in afurther example constitutes approximately 1-10 at. % in the ceramicmaterial.

In another example, the preceramic polycarbosilane or polycarbosiloxanematerial that results from the above-described reaction or reactions isthermally converted in an argon environment at a temperature of 1000° C.or greater for approximately two hours. The resulting ceramic materialis then crushed into a particulate material and further thermallytreated for approximately eight hours at a temperature of 1500° C. ineither generally inert or oxidizing environments, such as argon or air,respectively.

In another embodiment, the thermal treatment is applied to a mixture ofthe preceramic polycarbosilane or polycarbosiloxane material thatresults from the above-described reaction or reactions and another,different preceramic polymer. Alternatively, the ceramic powder thatresults after the thermal treatment at 1000° C. is mixed with anotherceramic powder, such as Si—O—C ceramic material and then furtherthermally treated at the 1500° C. temperature in either generally inertor oxidizing environments, such as argon or air, respectively.

In a further embodiment, prior to thermal conversion of the preceramicpolycarbosilane or polycarbosiloxane material, the material is mixedwith other, different preceramic polymers and/or additives. The selectedpreceramic polymer and/or additives will depend upon the desiredresultant ceramic material. In general, the additives can includemetallic materials and/or ceramic materials. In one example, thepreceramic polycarbosilane or polycarbosiloxane material is mixed with aceramic material and/or glass or glass ceramic material that includescarbides, oxides, nitrides, borides, silicides, oxycarbides,oxynitrides, carbonitrides, aluminides, silicates, titanates,phosphates, phosphides or combinations thereof. The glass andglass-ceramic materials may include silica, borosilicates, bariumaluminosilicates, lanthanum aluminosilicates, strontium magnesiumsilicates, barium magnesium aluminosilicates, calcium magnesiumaluminosilicates and lithium-containing glasses. The metal may include asuperalloy material, for example.

In a further embodiment, the preceramic polycarbosilane orpolycarbosiloxane material, or mixture with another, differentpreceramic polymer and/or additive, is then further processed to producea ceramic material. The ceramic material may be a coating or a layerthat is applied onto a component, a filler that is incorporated into amatrix of another material, a matrix that is filled with another,different material, or as a standalone, self-supporting body. In someexamples, the ceramic material that is produced from the preceramicpolycarbosilane or polycarbosiloxane material may be a combustionchamber, a turbine vane, compressor blade or vane, blade outer air seal,other component within a gas turbine engine or a portion thereof, forexample.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A method of treating a preceramic material, themethod comprising: providing a preceramic polycarbosilane orpolycarbosiloxane material that includes a moiety Si—O—M, where Si issilicon, O is oxygen and M is at least one metal; and thermallyconverting the preceramic polycarbosilane or polycarbosiloxane thatincludes the moiety Si—O—M material into a ceramic material.
 2. Themethod as recited in claim 1, wherein thermally converting thepreceramic polycarbosilane or polycarbosiloxane material produces aceramic material having a composition SiO_(x)M_(z)C_(y), wherein x<2,y>0 and z<1 and x and z are non-zero.
 3. The method as recited in claim1, wherein the at least one metal is selected from the group consistingof aluminum, boron, alkaline earth metals, transition metals, refractorymetals, rare earth metals and combinations thereof.
 4. The method asrecited in claim 1, wherein the at least one metal is selected from thegroup consisting of aluminum, boron and combinations thereof.
 5. Themethod as recited in claim 1, wherein the at least one metal is atransition metal selected from the group consisting of titanium,zirconium, hafnium, vanadium, chromium and combinations thereof.
 6. Themethod as recited in claim 1, wherein the at least one metal is arefractory metal selected from the group consisting of niobium,tantalum, molybdenum, tungsten, rhenium and combinations thereof.
 7. Themethod as recited in claim 1, wherein the at least one metal is a rareearth metal selected from the group consisting of scandium, ytterbium,gadolinium, yttrium, lanthanum, neodymium, dysprosium, lutetium andcombinations thereof.
 8. The method as recited in claim 1, wherein theat least one metal is an alkaline earth metal selected from the groupconsisting of barium, strontium, calcium, magnesium, and combinationsthereof.
 9. The method as recited in claim 1, wherein the at least onemetal includes aluminum.
 10. The method as recited in claim 1, whereinthe ceramic material from the thermal converting includes 0.5-20 at. %of the at least one metal.
 11. The method as recited in claim 1, whereinthe ceramic material from the thermal converting includes 1-10 at. % ofthe at least one metal.
 12. The method as recited in claim 1, furthercomprising crushing the ceramic material from the thermal converting toproduce a particulate material.
 13. The method as recited in claim 12,further comprising thermally treating the particulate material in aninert environment.
 14. The method as recited in claim 12, furthercomprising thermally treating the particulate material in an oxidizingenvironment.